What is the difference between "px", "dp", "dip" and "sp" on Android?

in
Inches - based on the physical size of the screen.
1 Inch = 2.54 centimeters

mm
Millimeters - based on the physical size of the screen.

pt
Points - 1/72 of an inch based on the physical size of the screen.

dp or dip
Density-independent Pixels - an abstract unit that is based on the physical density of the screen. These units are relative to a 160
dpi screen, so one dp is one pixel on a 160 dpi screen. The ratio of
dp-to-pixel will change with the screen density, but not necessarily
in direct proportion. Note: The compiler accepts both "dip" and
"dp", though "dp" is more consistent with "sp".

sp
Scale-independent Pixels - this is like the dp unit, but it is also scaled by the user's font size preference. It is recommend you
use this unit when specifying font sizes, so they will be adjusted
for both the screen density and user's preference.